Water-soluble substrates are gaining wider acceptance for use as packaging materials. Packaging materials include films, sheets, blown or molded hollow bodies (i.e. sachets, pouches, and tablets), bottles, receptacles and the like. Often, water-soluble substrates, when used in the preparation of certain types of these articles such as sachets and pouches, leak and/or become sticky when exposed to small amounts of water or high humidity. This can make them unsuitable for usage in the packaging and storage of the compositions contained therein.
The most common consumer complaint for water-soluble pouches is linked to unwanted pouch dissolution when accidentally exposed to small amounts of water, such as when water gets inside the outer packaging in which the pouches are sold and stored after purchase, from wet hands, high humidity, leaking sinks or pipes during storage. This may cause the water-soluble pouches to leak prior to use and/or stick together. The second most frequent complaint is that of the water-soluble pouch failing to fully dissolve upon use. Thus, there remains an unmet need for water-soluble substrates and articles made therefrom, such as sachets and pouches, which have improved resistance to dissolution against exposure to small amounts of water, yet can dissolve very quickly when immersed in an aqueous solution, such as rinse and/or wash water.
There is also a tendency to reduce the thickness of the water-soluble substrates not only to improve the dissolution in use, but also to manufacture water-soluble substrates and articles made therefrom at lower cost. However, as water-soluble substrates become thinner, their resistance to dissolution decreases.
Various methods are known in the art to retard the dissolution of water-soluble substrates. Typically, these methods involve coating the water-soluble substrate with a water-insoluble material. U.S. Pat. No. 6,509,072 describes a water-soluble substrate comprising a barrier coating. The barrier coating is a polymeric film which forms a continuous film on the water-soluble substrate. Another example of a barrier coating is described in WO 01/23460, assigned to Kao Corporation, wherein a surface of the water-soluble substrate is coated with a particulate or fibrous water-insoluble material wherein the amount of the water-insoluble material used is 0.1-80 parts per 100 parts by weight of the water-soluble film. These barrier coatings of the prior art are applied at a low amount and are relatively thin with respect to the thickness of the water-soluble substrate. These coatings may however not be sufficient to provide said substrate with sufficient resistance to dissolution after exposure to accidental water contact. This is especially the case when thin water-soluble substrates are to be used.
It is therefore an aspect of the present invention to provide a water-soluble substrate having improved resistance to dissolution prior to being immersed in water, independent of the thickness of the water-soluble substrate, yet can subsequently dissolve very quickly when immersed in an aqueous solution, such as rinse and/or wash water.